Sliding doors and windows of the lift and slide type are well known, and basically comprise:                a fixed frame;        at least one mobile frame or sash which slides horizontally, opening and closing relative to the fixed frame;        at least one sliding unit or carriage pair associated with the bottom horizontal member of the sash, resting on a horizontal base track and designed to enable the sash to slide in both directions;        a controlling member located on the sash and designed to control operating means for lifting the sash from the carriage (thereby moving the sash seals away from the track) so that it can then be slid open, and lowering the sash when it is back in the closed position, thereby returning the door/window to a sealed condition;        closing means acting between the vertical member of the sash and the vertical member of the fixed frame (which, in the closed configuration, abut against each other edge to edge).        
It is also known that doors and windows of this type—but also traditional sliding doors and windows—can be fitted with an accessory consisting of at least one contact element or insert known in the jargon of the trade as “anti-lifting plug” to provide added protection and security.
This accessory is normally connected to the door or window, especially if the door or window separates an interior room from the outside, particularly on low storeys of a building (such as separation of the room from a garden).
These anti-lifting plugs comprise a base which can be connected to the sash profile and a peg or plug which is joined to or forms a single body with the base, and which projects from the sash profile zone (in particular that forming the upper horizontal member) opposite the corresponding inner zone of the fixed frame profile.
The anti-lifting plug is applied on the sliding sash to prevent it from being lifted and/or pulled up out of its lower guides: such lifting could cause the sash to fall accidentally during an incorrect operation, but above all, it could be the result of prowlers attempting to break in from the outside.
In doors and windows of the “lift and slide” type, considered here, anti-lifting plugs are used rarely because they are less effective than they are on traditional sliding doors and windows where, by comparison, they are used more much more frequently. In practice, in the plugs used up to now on “lift and slide” doors and windows, the working thickness which comes into contact with the fixed frame must be less than that of plugs applicable to traditional sliding doors and windows: if that were not so, the plug would prevent the sash from being lifted in order to open it.
When the sash is lowered and closed, however, the reduced thickness leaves a relatively large gap between the plug and the profile, enabling unwanted lifting of the sash even if closed.
Another drawback is that the anti-lifting plug, when fitted, can only be applied on the upper corner of the sash, close to the side in which the operating means and closing means are located, since the plug cannot be fitted to the sash until the sash has been installed on the respective fixed frame equipped with the tracks. This is because the presence of the plug would prevent normal installation operations.
Now the problem is that attempts to lift the sash may be tried on the opposite side of the sash to that fitted with the anti-lifting plug. In such a case, the lifting action, even though less simple, could still cause the sash to come out of the tracks, meaning that it could be forced open. This is more critical if the sash has large dimensions, both in height and length.
At present, the possibility of fitting an anti-lifting plug on sliding sashes of this type is unfeasible, since the upper corner of the sash furthest from the corner zone fitted with the anti-lifting plug is closed beforehand by a guard profile extending along the entire vertical member of the sash. This is designed to keep these zones closed without interruption, avoiding the entry of external agents and improving the appearance of the door or window as a whole.